1. Field of the Invention
The present invention relates to catheters which are inserted into blood vessels and are used for diagnostic purposes or for medical treatment.
2. Description of the Prior Art
Intravascular catheters are employed in medical applications for a variety of diagnostic and treatment procedures. These include the injection of radiopaque dye, the use of balloon catheters, the use of laser catheters, etc., in arteries in the heart, brain, abdominal and peripheral areas. Guiding catheters are used in placing balloon and laser catheters and other medical devices into the desired artery. Typically, the catheter being used in the diagnostic or treatment procedure, or the guiding catheter to be used for guiding the balloon or laser catheter, is inserted into an artery in the leg or arm of the patient and threaded, often with the aid of a guidewire in the catheter, through various arteries until the leading tip of the catheter reaches the desired location. The end of the catheter and/or the end of the guidewire is formed with a desired curvature so that by rotating the catheter about its longitudinal axis during insertion, the catheter can be inserted into the desired arterial branches to reach its destination. The tip or distal end section of the catheter is formed from a relatively flexible and soft material to avoid injury to the walls of the arteries and to enable flexing for insertion into the desired arterial branch.
The body portion of the catheter must have high torsion modulus and column strength with desired flexibility to negotiate a tortuous path through the arteries without buckling. The high torsion modulus or rigidity is needed to transmit rotary motion from the proximal end to the distal end of the catheter; with a relatively lower torsion modulus, rotation of the proximal end creates spring torsion force in the catheter until the resistance to rotation of the distal end is overcome and the distal end suddenly flips or rotates past its intended angle of rotation. Thus the higher the torsion modulus in the length of the catheter without changing flexibility, the easier it is for the physician to direct the catheter to its intended destination. High column strength or resistance to compression in the longitudinal direction is needed to enable the advancement of the catheter along the arteries or to advance medical devices in the guiding catheters against frictional resistance.
High torsion modulus and column strength can be produced in catheters by forming the body portion with a stainless steel braid between inner and outer tubular layers having desired flexibility, or by forming the body portion from a tubular material having the desired torsion and column rigidity. Typical materials employed in forming the inner and outer layers in prior art braided catheters include polyurethane or polyethylene. U.S. Pat. No. 4,563,181 to Wijayarathna et al. discloses forming the body portion of the catheter from nylon-11; a soft tubular tip formed from a blend of nylon-11 and an ester linked polyether-polyamide copolymer commonly known as polyether block amide (PEBA) is fused onto the distal end of the tubular body portion.
The use of a coating of hydrogel material including polyvinylpyrrolidone-polyurethane interpolymer on catheters to reduce insertion friction and to reduce thrombogenicity is disclosed in U.S. Pat. No. 4,100,309 to Micklus et al. The disclosed hydrogel material has been successfully coated on polyurethane catheters and silicone wound drains. It has been disclosed that the hydrogel material will also adhere to polyvinyl chloride, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polytetramethylene terephthalate, latex rubber and polyisoprene. The hydrogel material can be applied to fluorocarbons and polyolefins which have been subjected to surface preparation to assure adequate wetting and bonding of the coating. The coating, when exposed to water, swells and develops a low coefficient of friction.
Although prior art intravascular catheters and the techniques for their employment have improved over the past several years, they have left a need for further improvement to enable optimization of catheter properties. Limited ranges of rigidity, flexibility and strength of materials possessing anti-thrombogenic and other blood compatible properties result in limitations on torsion modulus, column strength and flexibility of prior art intravascular catheters. Further the prior art catheters are subject to being expensive to manufacture.
Guiding catheters in particular require inner surfaces having a low coefficient of friction so that guidewires, balloon catheters, laser catheters, and other medical devices can be easily inserted and positioned in the arteries of the heart, brain or abdominal areas. Conventionally, such catheters have an inner layer formed from a fluoro polymer, such as polytetrafluoroethylene, fluorinated ethylene propylene copolymer, or a perfluoroalkoxy resin. The outer layer of the catheters are usually made of polyurethane or polyethylene, and braid wires are often interposed between the two layers to provide a suitable torsion modulus and column strength.
Such prior art guiding catheters have several deficiencies such as being expensive, having a small lumen, and losing their mechanical properties. Because of the dissimilarity between the materials of the inner and outer layers, extra steps, such as etching and applying adhesives are required to try to bond the two layers. In addition, extrusion of fluoro polymers requires special equipment and environmental control. This results in increased costs. The fluoro/urethane and fluoro/ethylene composites are generally softer than other polymers used in catheter bodies, and thus thicker walls, for example 0.014 to 0.018 inches (0.35 to 0.46 mm), are needed to provide the desired mechanical strength. This reduces the maximum size of lumen for a given size of catheter outer diameter to limit the size of medical device and the amount of contrast medium that can pass through the catheter. Further, fluoro polymers soften at body temperature and lose rigidity and preformed curvature to make their use more difficult.